A systematic review of the anxiety-alleviation benefits of exposure to the natural environment.

Research suggests that exposure to natural environments can be beneficial for health, such as reducing physical illness and improving mood and cognitive ability. The potential benefits of nature have come into focus at a time when mental health issues are growing globally. Here, we have selected 24 studies from four databases for meta-analysis to explore the effects of exposure to the natural environment on the anxiety of the human body and summarize the influencing factors on the anxiety relief effect. A random-effect meta-analysis of anxiety state changes before and after exposure to natural environment shows that natural exposure effectively alleviated human anxiety (SMD -1.28, 95% CI: -1.65 to -0.92). The overall quality of the included papers, assessed using the PEDro scale, is considered to vary considerably, but most of the papers are rated between 4 and 7 which is considered fair or good. In addition, we have also investigated the potential moderators of anxiety-relieving effects of the nature. Our results shows that the age and exposure time of the subjects are related to the effect of anxiety relief. The results of the subgroup analysis of moderators prove that compared with the middle-aged people (SMD -0.63, 95% CI: -1.13 to -0.12), young people (SMD -1.50, 95% CI: -1.90 to -1.10) get better anxiety alleviation effect in the natural environment. In terms of exposure time, compared with 0.5-2 h (SMD -0.18, 95% CI: -0.59 to -0.23) and >2 h (SMD -0.84, 95% CI: -1.40 to -0.27) exposure periods, subjects get the maximum anxiety relief benefit when they spent <0.5 h (SMD -1.60, 95% CI: -1.93 to -1.27) in the natural environment. However, the quality of the included studies varies greatly and there is a significant heterogeneity in the meta-analysis. Study location, natural environment type and other moderator factors have no obvious correlation with anxiety-alleviation effect of the nature. A higher quality and more comprehensive study needs to be carried out to find out more moderators about the effects of the natural environment on anxiety alleviation. Further experimental studies should also be conducted to determine the mechanism by which natural exposure reduces anxiety so as to provide strong support for the construction and improvement of healthy natural environment.